1. Field of the Invention
This invention relates to an automatic gear-type transmission apparatus, in particular for a motor vehicle, for changing transmission ratio without interrupting the transmission of a rotational torque between an engine shaft and a driven shaft.
2. Description of Related Art
A gear-type automatic transmission has been proposed in the past, which is equipped with a double clutch that couples the output shaft of an internal combustion engine to two input shafts of the transmission, one of which carries driving pinions for the first, third and fifth transmission ratios, while the other one carries the driving pinions for the second and fourth, and for the sixth if any, transmission ratios, while the driven pinions for these ratios are mounted for free rotation on an output shaft of the transmission and are in constant engagement with the corresponding driving pinions. Synchromesh means are associated with the driven pinions for coupling them selectively with the output shaft.
In this known apparatus, when a transmission ratio is engaged, the clutch mounted on the input shaft carrying the driving pinion for that transmission ratio is engaged, and the clutch mounted on the other input shaft is disengaged. In order to change from a first transmission ratio to a second transmission ratio it is necessary to carry out an initial preselection operation, by coupling the driven pinion for the second ratio to its shaft by a synchronisation step followed by a meshing step. In a second operation, the two clutches must be controlled together so as simultaneously and progressively to reduce the torque transmitted by the clutch of the first transmission ratio, and to increase the torque transmitted through the clutch of the second transmission ratio, which corresponds to xe2x80x9chuntingxe2x80x9d of the clutches.
To this end, it is necessary to provide means for real-time measurement of the velocities or accelerations of the shafts. A computer receives the output signals from these measuring means and produces control signals for rapid actuators of the clutches and synchromesh means, and the duration of a change of ratio must be less than 0.5 to 1 second approximately according to circumstances, and cannot be too short (which would present problems of energy transfer), or too long (which would cause prolonged slipping of the clutches and absorption of energy).
A main object of the invention is to avoid these drawbacks in an automatic gear-type transmission.
To this end, it proposes an automatic gear-type transmission apparatus, in particular for a motor vehicle, adapted to couple an engine shaft and a driven shaft together, and comprising at least one input shaft, at least one clutch arranged between the engine shaft and the output shaft, driving pinions mounted on the said input shaft and driven pinions mounted on the driven shaft, each driven pinion being in constant engagement with a driving pinion and defining a transmission ratio, one of the pinions for each ratio being fixed to the shaft on which it is mounted while the other pinion for the said ratio is freely rotatable on its shaft, and means for selectively coupling each free pinion fixedly with the shaft on which it is mounted, for engagement of the corresponding transmission ratio, characterised in that it has two input shafts and two clutches, each of which couples one input shaft to the engine shaft, with each input shaft carrying at least one driving pinion, and in that the selective coupling means comprise, for at least one free pinion, two controlled one-way lock-up mechanisms, mounted in opposition to each other between the free pinion and its shaft, and each able to occupy two positions, namely a rest position and a working position in which one of the mechanisms prevents the pinion rotating faster than its shaft, while the other one prevents the pinion rotating more slowly than its shaft, and mechanical means for actuating the lock-up mechanisms, the said actuating means comprising cams which are displaceable in straight line motion and/or in rotation.
The use of cams for control of the one-way lock-up mechanisms of the free pinions offers the advantage of positive control, guaranteeing actuation of the mechanisms by the displacement of the cams.
According to another feature of the invention, the apparatus comprises means for controlling the said clutches and the said actuating means enabling the transmission ratio to be changed without interrupting the transmission of a rotational torque between the engine shaft and the driven shaft, the change from a first to a second transmission ratio comprising maintaining a first mechanism in use and putting in the rest position a second one-way lock-up mechanism of the free pinion for the first ratio, bringing a first one-way mechanism for the said second ratio into use, performing at least one controlled clutch operation, putting the second mechanism for the first transmission ratio into its rest position, and bringing the second mechanism for the second transmission ratio into use. In the apparatus according to the invention, the change of transmission ratio takes place without hunting in the clutches, and thereby avoids all the above-mentioned disadvantages of the prior art.
According to yet another feature of the invention, the control sequence for the one-way lock-up mechanisms is the same for all the changes of transmission ratio.
In other words, the first and second lock-up mechanisms of the free pinions for the various transmission ratios will always be actuated in the same way and in the same order regardless of the transmission ratio being changed, and this greatly facilitates automatic control of the apparatus according to the invention.
As a result, the means for actuating the one-way lock-up mechanisms for the various free pinions can be governed by a single actuator.
In one preferred embodiment of the invention, the driving pinions for the transmission ratios are mounted alternately on the two input shafts, for example the driving pinions for the first, third and fifth ratios on the first input shaft and the driving pinions for the second, fourth and sixth ratios on the second input shaft.
Depending on the circumstances, the free pinions may be the driving pinions, mounted on the output shaft of the apparatus, or they may be the driving pinions mounted on the input shaft or shafts of the apparatus, or they may even comprise some driving pinions mounted on the input shaft or shafts and some driven pinions mounted on the driven shaft, depending on the torque to be transmitted, overall size, and other considerations relating to the mounting of the one-way lock-up mechanisms and their actuation.
In a preferred embodiment, the actuating means for the one-way lock-up mechanisms comprise at least one cam, which is mounted inside the shaft that carries the said free pinions and which is connected to an actuator by means of an axial rod.
Where the apparatus according to the invention has two input shafts as indicated above, the actuating means comprise two cams, one for locking and unlocking the free pinions for the ratios in respect of which the driving pinions are on the first input shaft, and the other one for locking and unlocking the free pinions for the transmission ratios in respect of which the driving pinions are on the second input shaft.
Each cam acts on the one-way lock-up mechanisms by means of pushers, which are for example mounted in radial apertures in the tubular wall of the shaft that carries the above-mentioned free pinions.
The one-way lock-up mechanisms are arranged between the internal rows of teeth of the said free pinions and the above mentioned shaft, and they include pawls associated with return springs and with the pushers which are controlled by the cams and which are arranged to come into engagement, in a predetermined direction of rotation, on the rows of internal teeth of the free pinions or to be displaced away from the said teeth, respectively.
In accordance with further features of the invention:
each cam is coupled in rotation with the shaft on or in which it is mounted,
each cam is displaced in axial straight-line motion by means of a leadscrew and nut system, the leadscrew of which is coupled to an actuator, such as for example an electric motor, the nut of the system being fixed to the cam or consisting of the latter,
in another version, each cam is fixed in rotation,
the one-way lock-up mechanisms for a free pinion are located on either side of the said pinion,
in another version, the one-way lock-up mechanisms for a free pinion are on the same side of the said pinion,
the two clutches of the apparatus according to the invention are of the type that operates dry, and are disposed on the outside of a casing containing the said pinions,
in a further version, a said clutch is a dry clutch on the outside of the casing containing the said pinions, while the other clutch is a multidisc clutch in oil, and is inside the said casing.
According to still a further feature of the invention, the apparatus includes a reverse gear pinion mounted on the input shaft that carries the driving pinion for the first transmission ratio, an intermediate pinion coupling the reverse gear pinion to a driven pinion mounted on the driven shaft, and controlled means for coupling together either the reverse gear pinion and the input shaft, or the driven pinion and the driven shaft.
In that case, the controlled coupling means may comprise synchronising means and meshing means of a conventional type.
In modified versions, the selective coupling means for the free pinions in forward gears are all one-way lock-up mechanisms of the above mentioned type, although some of them may be of this type with others being meshing means of a conventional type.
In general terms, the apparatus according to the invention combines the advantages of automatic transmissions with fluid couplings and epicyclic gear trains with those of manual gearboxes, while avoiding their respective disadvantages.
The apparatus is preferably associated with means for absorbing vibrations, arranged either on the engine shaft or on the input shafts of the apparatus.